In present systems, such as transmissions and motors for heavy industrial equipment, it is desirable to determine or monitor the speed of rotation of certain objects within the systems. Typically, a fixed sensor is attached to or on a casing associated with the system to measure the rotational speed of an object to be monitored. Although such a fixed sensor is acceptable for most speed sensing applications, there are situations where a fixed sensor is unable to accurately measure the speed of rotation of an object. For example, measuring the speed at zero speed or in the near zero speed region cannot be accomplished with such fixed sensors. Additionally, such fixed sensors cannot provide a high sampling or update rate at zero speed or near zero speed. Currently, in order to achieve the sampling rate, tone wheels or gears having a plurality of teeth have to be used. These help to provide a sampling rate in the medium to low speed region but does not solve the sampling rate problem in the extremely low speed region, especially at the zero speed point. Another problem associated with fixed sensors is sensing directional rotational speed requires quadrature decoding hardware. Directional rotational speed sensing is needed in transmission systems, hydraulic motor systems, and low speed marine diesel motor systems, for example. Currently, phase differential dual sensor quadrature decoding scheme is used to handle directional rotational speed sensing which requires two dedicated sensors.
In view of the above, it would be desirable to provide a sensing device which is capable of accurately measuring the rotational speed of an object at any speed. Further, it would be advantageous to provide a sensor device which is capable of providing a high sample rate at zero speed or in the near zero speed region.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.